As a characteristic, which has been hitherto requested for lubricating oils for automobiles and industrial machines, there is given a relatively high viscosity. Along with a recent improvement in performance of automobiles or industrial machines, further improvement in performance has been requested for those lubricating oils as well. With regard to the improvement in performance of the lubricating oils, developments of various synthetic lubricating oils have been conventionally known. For example, the following technologies have been known about an α-olefin polymer as one kind of component of the synthetic lubricating oils.
Patent Documents 1 and 2 each disclose a method of polymerizing 1-decene with a Friedel-Crafts catalyst using aluminum chloride or boron trifluoride. In addition, an example in which ethylene or an α-olefin is polymerized by any one of the various methods and the resultant polymer is used in a lubricating oil has been known. For example, Patent Document 3 discloses a production method involving the use of a reduced chromium catalyst, Patent Documents 4 and 5 each disclose a production method based on cationic polymerization, Patent Documents 6 and 7 each disclose a production method involving the use of a Ziegler type catalyst, and Patent Documents 8 to 16 each disclose a production method involving the use of a metallocene catalyst.
As described above, various technologies have been conventionally known about a method of producing an α-olefin polymer. However, characteristics requested of the lubricating oils have become more and more sophisticated, and hence additional technological development has been requested of the method of producing an α-olefin polymer. That is, improved fuel efficiency, reduced energy requirements, and a lengthened lifetime have been demanded of each of the lubricating oils in order that the lubricating oils may correspond to recent environmental problems. Accordingly, easy production of an α-olefin polymer capable of corresponding to those problems has been requested. In addition, an ability to produce assorted α-olefin polymers is preferred for providing an optimum lubricating oil in accordance with each of friction conditions and the like. For example, a production method by which the characteristics of an α-olefin polymer can be widely changed through the control of reaction conditions has been desired.
None of the above conventional production methods suffices in such situations. For example, a polymer obtained with the Friedel-Crafts catalyst is poor in viscosity index, low-temperature flowability, and durability. In addition, there have also been problems that boron trifluoride is expensive, and further, discharges fluorine having apparatus corrosiveness. In addition, various problems remain in the production methods involving the use of the other catalysts as well. For example, problems concerning the characteristics of the polymer are problems concerning its molecular weight and low-temperature characteristic. In addition, problems concerning the production methods are, for example, a problem concerning polymerization activity, a problem concerning ethylene as an essential component, a problem concerning a reaction condition such as a high pressure, the addition of a large amount of hydrogen, or a high reaction temperature, a problem concerning dilution with an inert solvent, and a problem concerning an expensive catalyst. As described above, even when any one of the conventional methods of producing an α-olefin polymer is employed, it has been difficult to produce an α-olefin polymer suitable for a lubricating oil on an industrial scale with ease, and it has also been difficult to change the characteristics of the α-olefin polymer widely through the control of reaction conditions.
Patent Document 1: U.S. Pat. No. 3,149,178
Patent Document 2: U.S. Pat. No. 3,382,291
Patent Document 3: JP 09-508151 A
Patent Document 4: JP 08-505888 A
Patent Document 5: JP 2000-351813 A
Patent Document 6: JP 07-145205 A
Patent Document 7: JP 05-271339 A
Patent Document 8: JP 07-133234 A
Patent Document 9: JP 06-80725 A
Patent Document 10: JP 03-131612 A
Patent Document 11: JP 02-169526 A
Patent Document 12: JP 2006-176760 A
Patent Document 13: JP 2005-200454 A
Patent Document 14: JP 2005-200446 A
Patent Document 15: JP 2005-501957 A
Patent Document 16: WO 2007/011459